Spin- and time-resolved photoelectron spectroscopy and diffraction studies using time-of-flight momentum microscopes

Gerd Schönhense; Hans-Joachim Elmers

doi:10.1116/6.0001500

paper

Spin- and time-resolved photoelectron spectroscopy and diffraction studies using time-of-flight momentum microscopes

arXiv:2110.13832 · doi:10.1116/6.0001500

Abstract

Momentum microscopy (MM) is a novel way of performing angular-resolved photoelectron spectroscopy (ARPES). Combined with time-of-flight (ToF) energy recording, its high degree of parallelization is advantageous for photon-hungry experiments like ARPES at X-ray energies and spin-resolved ARPES. This article introduces into the spin-resolved variant of ToF-MM and illustrates its performance by selected examples obtained in different spectral ranges. In a multidimensional view of the photoemission process, spectral density function $ρ (k, E_{B})$ , spin polarization $P (k, E_{B})$ and related quantities of circular dichroism in the angular distribution (CDAD) are part of the complete experiment, a concept adopted from atomic photoemission. We show examples of spin-resolved valence-band mapping in the UV, VUV, soft- and hard-X-ray range. Spin mapping of the Heusler compounds Co $_{2}$ MnGa and Co $_{2}$ Fe $_{0.4}$ Mn $_{0.6}$ Si at $h ν = 6$ ~eV prove that the second compound is a half-metallic ferromagnet. Analysis of the Tamm state on Re(0001) using VUV-excitation reveals a Rashba-type spin texture. Bulk band structure including Fermi surface, Fermi velocity distribution $v_{F} (k, E_{F})$ , full CDAD texture and spin signature of W(110) have been derived via tomographic mapping with soft X-rays. Hard X-rays enable accessing large k $_{p a r}$ -regions so that the final-state sphere crosses many Brillouin zones in $k$ -space with different $k_{z}$ . At $h ν = 5.3$ ~keV this fast 4D mapping mode (at fixed $h ν$ ) revealed the temperature dependence of the Fermi surface of the Kondo system YbRh $_{2}$ Si $_{2}$ . Probing the true bulk spin polarization of Fe $_{3}$ O $_{4}$ at $h ν = 5$ ~keV proved its half-metallic nature. The emerging method of ToF-MM with fs X-ray pulses from a free-electron laser enables simultaneous valence, core-level and photoelectron diffraction measurements in the ultrafast regime.

JVST Special collection Commemorating Charles S. Fadley

Spin- and time-resolved photoelectron spectroscopy and diffraction studies using time-of-flight momentum microscopes

Abstract

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